This invention relates generally to aircraft, and, in particular, relates to engines for high altitude and long duration flight aircraft.
Aircraft capable of flying at very high altitudes such as at about 100,000 feet for extended periods of time such as 24 hours can perform many important missions such as communications/data relay, ELINT/COMINT, Airborne Early Warning, Tactical reconnaissance, surveillance, airborne targeting, battle damage assessment, defensive countermeasures, and ballistic/cruise missile defense support.
Some of the aircraft performing some of these missions are the U-2, TR-1, and the SR-71 aircraft although the flights are much shorter than 24 hours. The U-2 is a subsonic high altitude, long duration flight aircraft but its use is limited by payload package weight and by being manned. As presently configured, the U-2 is not equipped to perform a mission of 24 hours or greater. Even if the U-2 could maintain station for such a period the presence of a human may actually limit mission capability.
The primary missions envisioned for this class of aircraft are to be performed automatically with little or no intervention by the pilot. The pilot, then, is essentially superfluous for the nominal, nonemergency mission. A common rationale for the presence of a pilot is the human capability for dealing with unforeseen situations. It is believed that the high-altitude missions inherently present much less opportunity for application of this ability than do other military situations. High altitude makes surprise attack unlikely since any attacker must approach from below and can be as easily monitored electronically as can the condition of on-board equipment.
For a mission of 24 hours duration, several problems could arise in the performance of the pilot, assuming he is the sole occupant of the aircraft. Clinical studies done on sleep deprivation show that subjects kept awake show behavior problems ranging from accounts of irritability, inattention, uncooperativeness, and episodic rage. None of these characteristics is acceptable during a flight of a sensitive nature and can easily result in interruption of the mission, or worse.
Other studies show that pilot performance can be maintained at acceptable levels for 24-hour periods using alternating sleeping/waking periods. An auto-surveillance system would command the pilot's attention in event of emergency. The question is why the pilot so alerted has to be in the cockpit rather than at a console on the ground. Also, if airplane endurance were extended beyond 24 hours, which may be desirable and feasible, pilot physical limits on the overall system become severe.
Another consideration is that some high-risk missions could be undertaken by the unpiloted aircraft on which a commander would hesitate to commit a pilot. A policy of minimizing exposure of humans to potentially lethal situations is desired.